Compressor unloader



Feb. 28, 1961 A. B. NEWTON COMPRESSOR UNLOADER Filed June '7, 1956 TOR.

Motor ATTORNEY Q WM COMPRESSOR UNLOADER Alwin B. Newton, Wichita, Kans.(850 Clubhouse Road, York, Pa.)

Filed June 7, 1956, Ser. No. 589,946

10 Claims. (Cl. 230-31) This invention relates to a compressor unloader,and more specifically to an apparatus equipped with pressureresponsivemeans for regulating the operation of a compressor.

This application is a continuation-in-part of my copending application,Serial No. 502,417, filed April 19', 1955, now US. Patent No. 2,761,616.

One object of this invention is to provide means for delaying theloading of a compressor until after the motor driving the compressor isin operation. Another object is to provide apparatus for loading orunloading a compressor after a predetermined interval has elapsed, orafter a predetermined condition is satisfied. A further object is toprovide means for automatically regulating the capacity of a compressor,or a series of compressors, in accordance with the load thereupon. Astill further object is to provide a compressor valve structure having avalve seat movable between operative and inoperative positions withrespect to a movable valve member, and pressureresponsive means andfluid pressure means cooperating with the valve seat for coordinatingthe operation of the valve structure with the operation of compressordriving means. In this connection, it is a specific object to provideautomatic control means for interrupting the flow of pressure fluid tothe pressure-responsive means upon the occurrence of a predeterminedcondition. Another objeet is to provide hermetically sealed means formoving the valve seat of a compressor into and out of operatingposition. Another specific object is to provide pressureresponsive meanscooperable with the valve structure of a compressor unloader, thepressure-responsive means including one or more bellows for moving thevalve seat between operative and inoperative positions in response tochanges in fluid pressure. Additional objects and advantages will appearas the specification proceeds.

Embodiments of the invention are illustrated in the accompanyingdrawings, in which- Figure 1 is a partly diagrammatic sectional sideelevation showing a compressor and the unloading apparatus of theinvention; Figure 2 is a broken cross-sectional view taken along lines22 of Figure 1; Figure 3 is a partly diagrammatic broken sectional sideview of a modified form of the compressor unloading apparatus; andFigure 4 is broken sectional end view of the modified compressorunloading apparatus in unloaded condition.

The compressor A illustrated in Figure 1 comprises a casing 1 which hasa top portion divided by wall 2 into a pair of compression chambers 3and 4,. While only a pair of chambers is shown, it is apparent that agreater or smaller number may be provided, depending upon the particularuse for which the compressor is to be adapted.

The lower portion of the casing carries a crank shaft 5 which haseccentric portions 6 and 7, and which may be rotated by any suitablemeans as, for example, by an internal combustion engine. Connecting rods9 and 10 are slidably attached to the eccentric portions of the crankshaft 5 in the customary manner, as shown in Figure 1. Rods 9 and 10have bearings securing them atent O F Patented Feb. as, 1961 ICC topistons 12 and 13 which are slidably mounted within chambers 3 and 4,respectively.

A continuous chain 11 extends about one end of the shaft 5 and ispreferably connected to a gear-type pump 14 at the lower portion ofeasing 1. Since the pump structure is well known in the art, it isbelieved that a detailed description herein is unnecessary. Pump 14 isimmersed in a source of pressure fluid such as a pool of oil or otherliquid 15 at the bottom of easing 1, and drives the liquid into conduit16 upon the rotation of crank shaft 5.

The top portion of easing 1 encloses a pair of valve units 17 and 18through which fluid must pass to enter compression chambers 3 and 4.Since both of the valve units are substantially identical in structureand operation, only one of these units will be described in detail.Valve ,unit'17 comprises generally a tubular valve casing 19 having anopening 20 in its side wall leading into suction chamber 21. Anotheropening or flow port 22 at the lower end of the valve casing places thesuction and compression chambers in communication with each other.Extending inwardly within suction chamber 21 and substantially midwaybetween opening 20 and the open lower end of the valve casing is anannular ledge or stop 23.

Within the compression chamber is a movable valve seat member or cage 24which has the general configuration of a hollow cone having a tubularportion 25 extending downwardly from its base. The tubular portion ofthe cage has an outer diameter less than the diameter of the cones baseso that at the juncture of the tubular portion and the base of theconical portion, there is an outwardly projecting peripheral ridge 26adapted for abutting or seating against the annular ledge or stop 23 ofthe valve casing. As illustrated in Figure 1, the tubular and theshownbest in Figure 2, an elongated and flexible leaf valve member 30 issecured by rivet 31, or by any other suitable means, to the top wall ofcompression chamber 3. Preferably, the inner end of valve 30 is tightlyfitted in a notch 32 provided in wall 2. The opposite end of the leafvalve is fitted loosely in a recess 33 in the compressor casing wall sothat the valve member may flex downwardly within recess 33 to admit gasinto chamber 3, andlmay also flex upwardly within that recess whenpiston 12 executes its compression stroke. It will be noted that thewidth of the elongated leaf valve is less than the diameter of opening22 in the valve casing, but is greater than the diameter of flow passage28 through the movable valve cage. Moreover, as illustrated in Figure 1,when the valve cage rests upon ledge 23 of the casing, the annular valveseat 29 provided by the movable cage is substantially in line with thelower end of the valve casing, and is positioned to make sealing contactwith the flexible valve member.

In the top wall of the compression chamber, on each side of the flexiblevalve member, is an exhaust port 34 which extends upwardly into exhaustchamber 35. The gaseous fluids compressed in the compression chambers 3and 4 flow upwardly into this exhaust chamber through the exhaust ports,and leave this chamber through opening 36 in the casing wall. To preventfluid from reentering the compression chambers from exhaust chamber 35,I provide a flat valve spring 37 which is centrally riveted or otherwisesecured to the wall of the exhaust chamber. Normally, the end portionsof the flexible valve 37 cover exhaust ports 34 and seal the exhaustchamber. However, as the compressor pistons execute their upwardcompression strokes, the ends of the flexible exhaust valve alternatelyflex upwardly to permit entry of the compressed gas into the exhaustchamber.

In the embodiment shown in Figure l, the movable valve cages are rivetedor otherwise fastened to movable cup-shaped pistons 38, 39 whichconstitute pressure responsive means for shifting the valve cages orseats and which are slidably mounted within the piston chambers 40, 41of the respective valve casings. Each of the chambers is sealed bycovers 42 and 43, respectively, and these covers are apertured so thatthe chambers communicate with conduits 44 and 45. The valve cage andpiston units may be biased upwardly into unloading position by springmeans, such as springs 46a and 47a disposed between the cup-shapedpistons and the annular ledges provided by the valve casings.

A valve 46 is interposed between fluid flow conduits 44, 45 and 16 tocontrol the flow of pressure fluid (such as oil) to chambers 40 and 41.Valve 46 is equipped with a valve member 49 which is movable into any ofthree positions. When the valve member is in the lowest of the threepositions, pressure fluid can flow from conduit 16, through valve 46 andinto conduits 44 and 45 leading to both of the piston chambers 40 and41. When the member is in a second or intermediate position, asillustrated in Figure 1, the lower end portion of the member isinterposed between the openings for conduits 44 and 45, so that conduit44 communicates with inflow conduit 16 and conduit 45 communicates withbleed passage 51. Therefore, only one of the compressor units will beloaded when the valve member 49 is in its intermediate position. If themember is raised into its third position, it is believed apparent thatboth of the compressor units will be unloaded. If desired, a ball detentstructure 50 maybe provided for maintaining the valve member in any ofthe selected positions. For automatic control of the valve member, valvestem 47 is connected to a suitable automatic control meansdiagrammatically represented in Figure l by box 48. Relative movement ofthe control means and valve body is prevented by any suitable means,such as collar 48a which rigidly supports the control means upon thevalve casing. The control means may be any device which is responsive tosome condition which is aflected by the compressors operation.

The operation of my invention is as follows: When the compressor isidle, no pressure fluid is supplied by the pump 14 to the pistonchambers, and the valve cages or 'valve seat members are maintained inraised position by there is no load upon the compressor and there issubstantially no work performed by the driving means, such as aninternal combustion engine M.

As crank shaft rotation continues, oil or other pressure fluid is driveninto the piston chambers 40 and 41 by pump 14. Consequently, the pistons38 and 39 are forced downwardly to seat the valve cages upon the annularledges of the valve casings. When the valve cages are in loweredposition, as illustrated by the righthand valve unit shown in Figure 1,the flexible valve members will cooperate with the movable valve seatprovided by the cages to prevent the discharge of compression fluid fromthe compression chambers into the suction chambers. 30 flexes downwardlywithin recess 33 to admit gas into When piston 12 moves downwardly,spring valve,

Therefore, during the initial revolutions of crank shaft 5, i

a suction chamber 103 therein.

flow passage through the valve seat member, this flow passage will beclosed when the valve member flexes upwardly to seat against the annularseat 29 during the compression stroke of piston 12. Hence, thecompressed gas is discharged only through exhaust openings 34 and intoexhaust chamber 35. If desired, port 36 may be placed in communicationwith the condenser of a refrigeration system.

It will be further noted that the portion of the compressor casingdefining recess 33 also provides a stop for limiting movement of thespring valve 30 in its first or downwardly flexed position. Similarly,the lower surface of the valve casing about opening 22 provides a secondstop for limiting the upward flexure of the valve member when themovable valve seat is in raised position. Con sequently, the flexiblevalve member is capable of moving between a first position and a secondor raised position regardless of the position of the valve seat. Sincethe width of the valve member is less than the diameter of opening 22,however, re-entry of compression fluid into the suction chamber will beprevented only when the valve member is in its second position and thevalve sea is in its lowered position.

As pointed out above, the loading and unloading of the compressor may befurther controlled by valve 46 and control means 48. For instance, thecontrol means 48 may comprise a conventional thermostatic device whichis operably connected to the valve 46 to open (or close) that valve whenthe internal combustion engine or other driving means reaches apredetermined operating temperature. Alternatively, the control means 48may be responsive to humidity, pressure or conditions affected by theoperation of the compressor. It is to be understood that while Figure 1shows the valve unit connected by conduits 44, 45 and 16 to a pressurefluid reservoir in the bottom of the compressor casing, these conduitsmay lead to other pressure fluid sources, such as the crank case of theengine which drives the compressor (as shown in Figures 3-4, in whichcase the fluid will be supplied by fluid pressure means operateddirectly by the engine M, such as a lubricating pump.

A modification of my invention is presented in Figures 3 and 4 of thedrawings. This embodiment is substantially similar to the form of theinvention shown in Figures 1 and 2, except for the pressure-responsivemeans adapted to move the valve seat member for loading and unloadingthe compressor A.

Like the structure already described, the present embodiment comprises acompressor casing defining a compression chamber 101, and a valve casing102 having An opening 104 in the bottom wall of the valve casing placesthe suction and compression chambers in communication with each other.Directly below the valve casing and within the compression chamber is anelongated valve member 105 which extends across the opening 104. Thisvalve member is substantially identical to the leaf spring valve shownin Figures 1 and 2, and like the previously described valve member has afree end which may flex between two positions within casing 106.

Withinsuction chamber 103 is a movable valve cage or valve seat member107. The hollow cage is provided with a semi-spherical upper portion anda tubular lower portion of reduced diameter. As shown in the drawings,the upper portion of the cage is equipped with a plurality of openings108, and the bottom of the cage is open to provide an annular valve seat109. Hence, the cage provides a continuous flow passage therethrough forthe flow of pressure fluid between the suction and compression chambers.It is to be noted that the cage is equipped intermediate the lengththereof with a lateral ridge 111 adapted to rest upon annular ledge 112of the valve casing, and that the outer surface of the cages tubularlower portion slidably and sealingly engages the wall of the casingextending about opening 104.

Above the valve cage, and secured thereto by stud or rivet 113, is acup-shaped member 114 equipped with an outwardly extending lip 115 alongits top edge. A helical compression spring 116 extends between theoutwardly projecting lip or flange 115 and the lower inner surface ofthe valve casing, and urges the cup-shaped member and the valve cageinto the raised position shown in Figure 4.

The valve casing has a side opening 117 for the inflow of compressionfluid and a top opening 118 directly above the valve cage and cup-shapedmember. The diameter of the latter opening is smaller than the diameterof flange 115 so that the upper wall of casing 102 provides a stop forlimiting the upward movement of the valve cage assembly. Within thecup-shaped member 114 and extending upwardly through top opening 118 isa suction chamber sealing bellows 119. The bellows has the conventionalaccordion-folded side walls and is provided with a rigid bottom plate120. Preferably, the bellows is formed from metal and has its open endsoldered or otherwise sealingly secured to a connecting plate 122directly thereabove. A domelike cover or hood 123 is secured to both theconnecting plate and the valve casing by means of bolts 124 or by anyother suitable connecting means. A second bellows 125, larger thanbellows 119, is mounted within cover chamber 126, and is provided with arigid top plate 127 and the conventional accordion-folded metal sides.Most desirably, the lower edge of bellows 125 is turned outwardly andupwardly, and is sealingly secured to the inner surface of cover 123. Asshown in the drawings, gaskets 121 and 128 may be provided between theconnecting plate, the cover and the valve casing.

A depending shaft 129'is welded or otherwise secured to the top plate ofthe upper bellows 125, and extends downwardly through both of thebellows to engage the bottom plate of lower bellows 119. Preferably, thecentral opening 130 of the connecting plate is enlarged and is fittedwith a sleeve 131 which extends downwardly about the lower portion ofthe shaft 129 to guide the movement of the shaft and to protect theflexible wall of the lower bellows. It will be seen that the upper andlower bellows are, therefore, in communication with each other and havetheir interiors sealed from both the suction chamber 103 provided by thevalve casing, and the pressure chamber 126 provided by the cover. Ifdesired, the connecting plate 122 may be equipped with a bleed passage132 to provide outside reference pressure for the communicating bellows.

A fluid flow conduit 133 communicates with chamber 126 and is connectedat its opposite end through an automatic valve diagrammaticallyrepresented in Figures 3 and 4, and indicated by number 134. This valve134 corresponds with the control means 48 and valve structure 46 shownin greater detail in Figure 1, and constitute means for directingpressure fluid carried by conduit 135 either into conduit 133 or intobleed passage 136.

Pressure fluid for loading the compression structures shown in Figs. 3and 4 may be pumped from a reservoir in the compressor casing (as inFig. 1), or from any other source, such as the crank case of an enginedriving the compressor. Numeral 137 generally designates such an engineor motor crank case structure, represented somewhat diagrammatically andon a reduced scale in the drawings. As the crankshaft 133 rotates, thefluid pressure means comprising pump 139 drives oil from reservoir 140into passage 135. In the illustration given, a relief pressure-adjustingmeans is shown interposed along bleed passage 141 for regulating themaximum fluid pressure within chamber 126, and at the same time, forestablishing maximum operating suction pressure. The pressure-adjustingmeans comprises a ball valve 142 which is urged by spring 143 in aposition closing passage 141. The-tension of spring 143 may beselectively varied by adjustment of threaded cap 144-.

If conduits 135 and 136 are connected to the lubricating pump of adriving motor, then the compressor will remain in unloaded condition(Figure 4) until the motor and 18.

develops lubricating pressure greater than the pressure of thecompression fluid within the valve casing. More specifically, the forceof spring 116 and the pressure within suction chamber 103 will hold thevalve cage in a first or raised position until the oil pressure withinpressure chamber 126 is suflicient to overcome the forces suspending themovable valve seat. When the valve seat member is spaced from theflexible spring valve 105, as shown in Figure 4, compression fluid mayflow in both directions through flow passage 110, and consequently thecompressor will perform no work.

As the compressor driving means continues its operation, oil will flowthrough passages 135 and 133 and fill pressure chamber 126. Finally,when the force of the oil upon bellows 125 exceeds both the force of thecompression fluid upon bellows 119 and the upward force of spring 116,plate 127 of the upper bellows will be driven downwardly towards thevalve cage. The depending shaft carried by the pressure-responsivebellows abuts lower plate 120 so that as the upper bellows contracts,the shaft, the cup-shaped member 115 and the valve seat member 107 willbe shifted downwardly. When the valve cage or valve seat member reachesthe second or lowered position shown in Figure 3, the flexible valvemember will engage the annular seat of the valve cage as the compressorpiston executes its upward stroke, and will prevent compression fluidfrom re-entering the suction chamber. Therefore, the compressor will bein loaded condition.

Since the compressor will be loaded only when valve 134 is open andwhen, at the same time, downward force exerted by the pressure fluid isgreater than the upward force exerted by the compression fluid withinthe suction chamber plus the upward force of spring 116, the maximumoperating suction pressure may be easily controlled by adjustment of theoil relief pressure means. Should the force exerted by the suctionpressure plus the force of spring 116 exceed the force exerted by theselected maximum oil pressure as controlled by ball 142, bellows 119will contract and the valve seat will move upwardly to unload thecompressor. Thus, by adjusting the operating pressure of ball 142 byadjustment means 144, the maximum possible operating suction pressure ofthe compressor can be controlled.

Control of the compressors maximum suction pressure is especiallyimportant where, for example, the means for driving the compressorcomprises an internal combustion engine. Since such an engine normallyhas a falling torque curve as its speed is reduced, overloading of thecompressor cannot be tolerated. Hence, by providing a control upon themaximum suction pressure, the torque required to drive the compressorwill be automatically prevented from exceeding a predetermined amount.

While Figures 3 and 4 show only single compressor valve units brokenaway from the remainder of the compressor structure, it will beunderstood that a plurality of compressor cylinders might be groupedtogether, each of the cylinders being loaded and unloaded by individualvalve structures, as represented in Figure 1 by units 17 Control valve134 will then operate to sequentially load and unload the cylinder inresponse to conditions affected by the compressors operation, asdescribed above. If sequential loading and unloading of the cylinders isdesired in order to limit the torque requirements of the power sourceand to prevent the occurrence of too high a suction pressure, springs116 may be of different strengths in different valve units so that asthe suction pressure decreases, the cylinders will be successivelyloaded, one after the other. Further, it will be noted that the springs116 in one or more of the valve units may be omitted entirely. In such acase, where the spring force component is a suificiently large portionof the force which opposes the bellows 125, a cylinder without thespring would be loaded by the adjusted oil pressure even though thesuction pressure is relatively high. In a compressor having multiplecompression cylinders, the power demands of the loaded cylinder lackingthe spring 116 would be relatively low, and this cylinder would operateto reduce the suction pressure to a point where the sequential loadingof the remaining cylinders would not require an undue or prohibitiveincrease in driving torque or power. If desired, the valve assembly ofthe first cylinder of the group may be provided with a fixed valve seatso that, like conventional compressor cylinders, the first cylinder willbe permanently loaded during compressor operation.

It is to be understood that the difference between the diameter of thelarger bellows 125 and the diameter of the smaller bellows 119 generallycorresponds with the difference between the normal pressure of the oildelivered by the fluid pressure means 139 and the desired maximumoperating pressure of the compression fluid within the suction chamber.For example, if the lubricating oil pressure of the driving means isone-half the desired maximum suction pressure, then the area of plate127 should be no less than twice the area of plate 120. Therefore,during normal compressor operation, the downward force upon the upperplate will exceed the upward force upon the lower plate (including theforce of spring 116) of the pressure-responsive means, and the valveseat will remain in its lower operative position. Should the suctionpressure momentarily exceed the selected maximum, the valve seat willmove upwardly to relieve the excess pressure by temporarily unloadingthe compressor. Where the compressor is provided with multiplecylinders, sequential loading and unloading of those cylinders may beobtained by providing the respective valve units with bellows 125 ofsuccessively greater diameter or area. It is to be noted that if oilpressure during normal compressor operation substantially exceeds thegas pressure within the suction chamber, then the upper bellows 125 andshaft 129 may be eliminated so that the oil pressure directly opposesthe suction pressure at bellows 119. Under such conditions, the loadingand unloading of the compressor will result from the oil pressure beingalternately greater and less than the suction pressure.

While in the foregoing specification an embodiment of the invention hasbeen set forth in considerable detail pression chambers through a flowport, a movable valve member adjacent each of said flow ports, aplurality of valve seats each being shiftable between two positions andeach being cooperable with one of said'valve members for closing saidport only when said seat is in one of said two positions,pressure-responsive means cooperating with each of said seats toposition the same for independently loading and unloading each of saidcompressors, a motor for driving said compressor units, pressure fluidpumping means operably connected to said motor, pressure fluid passagemeans for delivering pressure fluid from said pump to saidpressure-responsive means, said pressure-responsive means comprising aplurality of pairs of opposing and internally communicating bellows ofunequal size, the smaller of said bellows of each pair being disposedwithin each of said suction chambers for exposure to the suctionpressure therein and the larger of said bellows of each pair beingsubjected to pressure fluid delivered by said pressure fluid passagemeans, said valve seats each being connected to a pair of bellows for r8 said bellows is compressed and into a loading position when thesmaller of said bellows is compressed, the size differential of saidpaired bellows being different for successive pairs for the sequentialunloading and loading of a plurality of compressor units.

2. A compressor unloading apparatus comprising a compressor having acompression chamber therein, a valve casing having a suction chambercommunicating with said compression chamber through a flow portextending therebetween, a valve seat having an outer periphery sealingsaid port and having a flow passage therethrough for the flow ofcompression fluid between said suction and compression chambers, saidseat being movable between first and second positions, a movable valvemem ber cooperable with said valve seat only When said seat is in saidsecond position for controlling the flow of compression fluid throughsaid flow passage, biasing means for urging said valve seat towards saidfirst position, pressure-responsive means operatively connected to saidseat for moving said seat between said first and said second positions,a fluid pressure source, pressure fluid passage means extending betweensaid source and said pressure-responsive means, and fluid pressure meansfor driving fluid from said source to said pressure-responsive meansalong said pressure fluid passage, said pressureresponsive meanscomprising a pair of communicating bellows, one of said bellows beingexposed to the pressure fluid carried by said passage means and theother of said bellows being exposed to compression fluid within saidsuction chamber, and means connected with said seat and with both ofsaid communicating bellows for moving said seat into said secondposition when said first-mentioned bellows is compressed and for movingsaid seat into said first position when said second-mentioned bellows iscompressed.

3. A compressor unloading apparatus comprising a compressor having acompression chamber therein, a valve casing having a suction chambercommunicating with said compression chamber through a flow portextending therebetween, a valve assembly operatively associated withsaid port and including a valve element movable between a first positionwherein fluid is permitted to flow in either direction between saidsuction and compression chambers and a second position wherein fluid ispermitted to flow only in one direction from said suction chamber tosaid compression chamber, pressureresponsive means operatively connectedto said valve element for moving the same between said first and secondpositions, means for delivering pressure fluid to saidpressure-responsive means, said pressure-responsive means comprising apair of opposing and internally communicating bellows of unequal size,one of said bellows having its exterior exposed to pressure fluiddelivered by said pressure fluid delivery means and the other of saidbellows having its exterior exposed to compression fluid within saidsuction chamber, said valve e l gment being operatively connected tosaid pressure-responsive means for movement into said second positionwhen said one bellows is compressed and for movement into said firstposition when said other bellows is compressed.

4. The structure or" claim 3 in which the size differential of said twocommunicating bellows is indirectly related to the predetermined normalpressure of said pressure fluid and the predetermined maximum pressureof said compression fluid.

5. The structure of claim 3 in which said one bellows is larger in sizethan said other bellows.

6. A compressor unloading apparatus comprising a compressor having acompression chamber therein, a valve casing having a suction chambercommunicating with said compression chamber through a flow portextending therebetween, a valve assembly operatively associated withsaid flow port and including a valve element movable between a firstposition wherein fluid is permovement into an unloadingtposition whenthe largerof mitted to flow ineither direction between said suction andcompression chambers and a second position wherein fluid is permitted toflow only in one direction from said suction chamber to said compressionchamber, pressure-responsive means operatively connected to said valveelement for moving the same between said first and second positions, apressure fluid source, pressure fluid passage means extending betweensaid source and said pressure-responsive means, and fluid pressure meansfor driving fluid from said source to said pressure-responsive meansalong said pressure fluid passage means, said pressure-responsive meanscomprising a pair of opposing and internally communicating bellows ofunequal size, the larger of said bellows having its exterior exposed topressure fluid carried by said passage means and the smaller of saidbellows having its exterior exposed to compression fluid within saidsuction chamber, said valve element being operatively connected tosaidpressure-responsive means for movement into said second position whenthe larger of said bellows is compressed and for movement into saidfirst position when the smaller of said bellows is compressed.

7. The structure of claim 6 in which the size diflerential between saidlarger and smaller bellows is indirectly related to the predeterminednormal pressure of said pressure fluid and the predetermined maximumpressure of said compression fluid within said suction chamber.

8. The structure of claim 6 in which a control valve is interposed alongsaid pressure fluid passage means for regulating the flow of pressurefluid from said source to said pressure chamber, said valve beingequipped with automatic control means for regulating the flow ofpressure fluid in response to changes in conditions resulting from theoperation of said compressor.

9. A compressor unloading apparatus comprising a compressor having acompression chamber therein, a valve casing having a suction chambercommunicable with said compression chamber, a movable valve seat withinsaid suction chamber and having a flow passage therethrough, said seatbeing movable between a first position and a second position, a movablevalve member cooperable with said valve seat only when said seat is insaid second position for controlling the flow of compression fluidthrough said flow passage between said suction and compression chambers,said valve casing also providing a pressure chamber for receivingpressure fluid therein, and pressure-responsive means extending be'tween said suction and pressure chambers, said pressureresponsive meanscomprising a pair of opposing and internally communicating bellows ofunequal size, the larger of said bellows projecting into said pressurechamber for external exposure to the pressure fluid contained therein,and the smaller of said bellows projecting into said suction chamber forexternal exposure to the compression fluid contained therein, connectingmeans connecting opposite ends of said communicating bellows so that theexpansion of one produces a contraction of the other, said valve seatbeing connected to said bellows for movement into said first positionwhen the larger of said bellows is expanded and the smaller of saidbellows is contracted and for movement into said second position whenthe larger of said bellows is contracted and the smaller of said bellowsis expanded, whereby, a relatively low fluid pressure within saidpressure chamber is capable of controlling the flow of compression fluidunder relatively high pressure within said suction chamber.

10. The structure of claim 9 in which the size differential of said twocommunicating bellows is indirectly related to the predetermined normalpressure of said pressure fluid within said pressure chamber and thepredetermined maximum pressure of said compression fluid within saidsuction chamber.

References Cited in the file of this patent UNITED STATES PATENTS534,813 Christensen Feb. 26, 1895 598,283 Christensen Feb. 1, 1898862,867 Eggleston Aug. 6, 1907 1,607,657 Whitehead Nov. 23, 19261,931,833 Sparacino Oct. 24, 1933 2,197,158 Saharoif Apr. 16, 19402,317,119 Stevens Apr. 20, 1943 2,555,005 Warneke May 29, 1951 2,761,616Newton Sept. 4, 1956

